Relationship of laboratory tests of rock bolt SCC to service failures of rock bolts

Abstract

The stress corrosion cracking of rock bolts has been explored using Linearly Increasing Stress Tests (LIST). In LIST testing, a sample is exposed to the environment of interest and the stress is slowly increased until failure. SEM examination of the fracture surfaces is used to help identify the fracture mechanism. Rock bolt steel subjected to LIST testing in air and distilled water showed ductile failure and a dimple rupture failure surface. In contrast, rock bolt steel subjected to LIST testing in dilute sulphate/chloride solutions showed subcritical crack growth followed by brittle fracture. Analyses of rock bolts, which have failed in service, have indicated similar failures. The LIST test in the sulphate pH 2.1 provides a good foundation for a test to mimic service SCC, to be used to study the influences of rock bolt metallurgy and to explore countermeasures to service SCC. The transgranular nature of the SCC fracture, and the fact that SCC occurs at room temperature in the sulphate pH 2.1 solution point to the likelihood that the SCC mechanism probably involves hydrogen. Current work is (1) exploring the details of the fracture mechanism, (2) carrying out a detailed fractographic comparison between the service failures and the sulphate pH 2.1 fractures, and (3) exploring the issue of environment specificity.